Some software applications require priority handling in the network that is to bear the traffic they generate. Examples of software applications that often require priority handling are applications for making voice-over-Internet-Protocol (VoIP) calls or gaming applications, such as GRID, commercially provided by NVIDIA Corporation of Santa Clara, Calif. QoS (Quality of Service) is the mechanism that plays an important role in establishing traffic priority. QoS employs quantifiable metrics, such as packet loss rate, packet delay and average bitrate, to define priorities for certain services. While the priorities apply all the time, they are especially useful during times of high congestion.
In an Evolved Packet System (EPS), i.e. a combination of a Long-Term Evolution (LTE) Radio Access Network and an Evolved Packet Core (EPC) network, QoS is implemented between User Equipment (UE) and Packet Data Network (PDN) gateways and is applied to a set of “bearers” called EPS bearers. As those skilled in the pertinent art understand, a “bearer” is a virtual entity, namely a group of network configurations, including an EPC and a Radio Access Network (RAN) part, that together defines QoS for a subset of traffic. The RAN part of the EPS bearer is realized by a Data Radio Bearer (DRB).
Two types of bearer are currently defined in an EPS: a default EPS bearer and a dedicated EPS bearer. At least one default EPS bearer is automatically provided with each PDN connection in LTE, usually providing “best-effort” QoS. A dedicated EPS bearer is created exclusively by the network to accommodate traffic with specific QoS needs, compared to the QoS provided by the default bearer. In the following, only one PDN is considered for simplicity, however the extension to several PDNs is straightforward.
A traffic flow template (TFT) is a set of rules used to route traffic to the correct EPS bearer. A default EPS bearer need not have a TFT, but a dedicated bearer always has a TFT. A TFT for a dedicated EPS bearer allows the UE and the network to determine the bearer that should bear a particular IP packet. TFT rules are primarily based on IP packet source and destination addresses. However, other information may be included, such as protocol type or port number.
A request for a certain QoS may be either UE-initiated or network-initiated. In a network-initiated request, an application requests a specific QoS through application level signaling using a default EPS bearer to an Application Function (AF) entity. The AF entity then sends Service Description parameters to a Policy Charging Rules Function (PCRF) in terms of QoS requirements. In response, the PCRF derives Policy Control and Charging (PCC) Rules and send them to a Policy and Charging Enforcement Function (PCEF). The PCEF then triggers the creation of one or more dedicated EPS bearers as needed.
In a UE-initiated request, an application requests specific QoS from a modem in the UE. Standardized AT commands are available for 3GPP access. The UE then sends a Bearer Resource Request (BRR) including its QoS requirements. The PDN gateway then forwards the BRR request to the PCRF. If agreed, the PCRF derives PCC rules and sends them to the PCEF. The PCEF then triggers the creation of one or more dedicated EPS bearers as needed.